Device-to-Device (D2D) communication facilitates direct communication between wireless communication devices. In some scenarios, the wireless communication devices operate within a radio access network. In other scenarios, the wireless communication devices themselves constitute the radio access network. With the possibility for wireless communication devices to communicate using direct D2D communication, the wireless communication devices need not be required to communicate via an infrastructure node, such as a cellular base station or a wireless access point.
In cellular network assisted device-to-device communications (also called D2D communications as a cellular underlay), wireless communication devices in the vicinity of each other can establish a direct radio link (D2D bearer). While the wireless communication devices communicate over the D2D “direct” bearer, they also maintain a cellular connection with their respective serving network node, such as a base station or eNodeB (eNB).
D2D communication can be used by a D2D capable wireless communication device to offer one or more services to other D2D capable wireless communication devices. These services are sometimes referred to as proximity services (ProSe). A few non-limiting examples of such services include (1) public safety and disaster relief, which may also be known as national security and public safety (NSPS) or public warning systems (PWS), (2) relaying function, (3) social networking, and (4) cooperative positioning.
Public Warning Systems (PWS) refer to a range of technical solutions and standards that facilitate warning the public in case of a disaster or public safety situation, such as an earthquake or large accidents, which can be manmade, natural, or accidental. An example of PWS in 3GPP for cellular communication, for example, includes wireless system parts and communication protocols called Earthquake and Tsunami Warning System (ETWS) that specifically addresses disaster situations due to earthquake, tsunami, or other natural catastrophes.
Relaying function refers to a D2D wireless communication device (an intermediate device) acting as an intermediate node capable of forwarding information received from one D2D wireless communication device (a source device) to another D2D wireless communication device (a destination device). The intermediate device may relay the received information to the destination device either transparently or after decoding and analyzing the contents of the received message.
Social networking refers to services in which the wireless communication devices can send and/or receive a wide range of personal data or information such as email, text messages, face book, etc.
Cooperative positioning refers to D2D wireless communication devices that exchange positioning related data or signals with their peers. Thus, not all devices need to be able to receive positioning signals from satellite infrastructure and/or ground based infrastructure. For example, users in a Global Navigation Satellite System (GNSS)-hostile environment, such as an indoor environment, or users without GNSS capability receive aiding data from other nearby GNSS capable users capable of determining their own position and assisting others to determine their positions.
In evolving LTE-Advanced and 5G cellular networks, D2D communication is useful in supporting proximity services (ProSe). Both the 3rd Generation Partnership Project (3GPP) and the METIS project have agreed on advanced mechanisms, including mode selection, power control, and resource allocation, that enable D2D technology to realize proximity services both under cellular network coverage and out-of-coverage situations. Specifically, there is a broad consensus that local communications (i.e., ProSe) should be supported for In Network Coverage (INC), Partial Network Coverage (PNC), and Out-of-Network Coverage (ONC) scenarios.
In the INC scenario, D2D wireless communication devices are under the full coverage of one or more network nodes. The D2D wireless communication devices are able to receive signals from and/or transmit signals to at least one network node. The D2D wireless communication device can also maintain a communication link with the network. The network can ensure that the D2D communication does not cause high interference to the cellular layer.
In the PNC scenario, at least one of the D2D wireless communication devices among the D2D devices involved in a D2D communication is under the network coverage and at least one of these devices is not under network coverage.
In the ONC scenario, none of the D2D wireless communication devices involved in a D2D communication are under network coverage. That is, none of these devices can receive signals from and/or transmit signals to any of the network nodes. ONC coverage is due to lack of network coverage in the vicinity of the D2D wireless communication devices or due to insufficient resources in the network nodes to serve or manage the D2D wireless communication devices. As a result, D2D wireless communication devices in the ONC scenario cannot receive assistance from network nodes and their interference cannot be managed by the network nodes.
A wireless communication device in Radio Resource Control (RRC) idle or RRC connected states can be in the INC or PNC scenario. A wireless communication device in the ONC scenario cannot be considered to be in RRC idle state or RRC connected state.
The coverage status of a wireless communication device can change. As an example, a wireless communication device may move from a geographical location outside the range of any network node (ONC scenario) to a geographical location within the range of a network node (INC scenario).
Radio Admission Control (RAC) allows for accepting or rejecting a Radio Bearer (RB) Setup Request (sometimes also called Evolved Packet System (EPS) or System Architecture Evolution (SAE) bearer service by the Core Network since RB in response to successful RAC is typically assigned by the core network). The RAC may also interchangeably be referred to as Admission Control (AC), radio access admission control, radio network admission control, network admission control, radio interface admission control, session admission control, call admission control, radio link admission control, radio bearer admission control or similar terms. For the sake of consistency hereinafter the term RAC is used. In the 3GPP LTE system, RAC is exercised by the base station, i.e., the eNB. The RAC algorithms are proprietary, but they are typically designed for maintaining the quality-of-service (QOS) of ongoing radio bearers (retain-ability) while ensuring high resource utilization and system stability. Specifically, the purpose of RAC is to admit SAE/EPS radio bearers (RB) as long as radio resources are available to provide QOS for in-progress RBs and for the newly arrived RB and also to ensure system stability.
RAC typically checks the availability of radio resources when setting up Guaranteed Bit Rate (GBR) radio bearers, for which—if admitted—a minimum (guaranteed) bit rate should be provided. Some rudimentary RAC may also be exercised for so called best effort SAE/EPS bearers in order to maintain system stability. RAC typically takes into account the available resources (UL, DL) as well as internal BS resources and the QOS class identifiers (QCI) of the ongoing bearers and the QCI of the radio bearer requested. In the 3GPP LTE system, for example, there are standardized QCIs for GBR and non-GBR services associated with delay requirements, packet error loss rate, and priority level.
In LTE, each bearer is associated with an allocation and retention priority (ARP) indicator that is used by the eNB in congestion situations to decide which bearer can be dropped (preempted) and which bearer must be maintained (retained). ARP is also used to make admission decisions of newly arriving RB requests. For example, an arriving high priority RB request can be granted by the eNB even in a congestion situation by preempting an ongoing low priority RB. A low priority RB can also be preempted in order to maintain the QOS of ongoing high ARP bearers.
Recently, the scope of RAC has been extended to the establishment of D2D communications. The basic idea of RAC for D2D is to utilize network control for assessing the resource situation and consequently the admissibility of D2D bearers for D2D communication in cellular spectrum and using cellular resources.